I was having a weird issue on my machine where it was turning on by itself after hibernating it. I double checked my "Power Management" settings for Mouse, Keyboard and other hardware devices and the "Allow this device to wake the computer" setting was already off.
Then, I went to Device Manager and started checking each item listed in the tree there.
Finally, after few minutes of traversing I was able to locate the exact item which was causing the issue for me and it was my Ethernet adapter connection i.e in my case it was "Intel(R) Ethernet Connection (2) 128-V". I went to its "Power Management" tab and noticed "Allow this device to wake the computer" checkbox was checked for me.
In order to fix my issue I unchecked that setting and I was no longer facing my issue.